Pain/saddle fit has been brought up and ruled out so I won't mention that.
I picked up a new horse a few months back - a young mare. She has quite the attitude. One of her "tricks" was to buck at the lope. Especially when she wasn't in the mood for it. :)
To be fair, some of it was probably pain related. She wasn't too muscled up on the left and likely had trouble maintain a lope to the left. My being a little off balance on left turns didn't help. With the help of some friends watching the situation we figured out the cause and solved that part of the problem.
Still, she would have some real rodeo moments when she didn't want to work.
You don't like the one rein stop, but the same "disengage" principle is how I solved the behavior side of it.
First, used properly the ORS is a safe procedure. It is not simply pulling the horse's head around and bringing the horse off balance. My horse has great lateral flex and will easily bring her head to your knee on either side with a very soft rein. That lateral flex really helps when you need to disengage the hips.
Since my mare was protesting work, it was pretty easy to predict when the bucking would start. Knowing it was coming, I was prepared and ready. The instant I felt a buck coming on, I would pull her head around, left or right - doesn't matter. (It is hard to explain. It is more of a very sharp turn or "about face." The horse doesn't want to fall over either so she ends up turning rather than bucking. You end up disengaging the hips rather than fighting with the horse. It is done with very little rein and mostly body movement.) From there, I would so 20-30 seconds of "hips over" (basically a spin where the front legs keep position and the back legs move).
Sometimes, I would do hips over and then some serpentines.
The basic idea is to interrupt the buck (ideally before it occurs) and then make the horse work hard. After a few times, the horse will learn "thinking of a buck" = "I have to do too much work." The old "make the right thing easy and the wrong thing hard" concept. As with any behavior training, timing of the correction is very important.
If the horse is bucking to avoid work, you have to make the correction tougher than the work being avoided. When you feel the buck coming on, work the horse hard for 20-30 seconds. When you get a good lope, only lope for a few strides and then break down and reward the horse (pet, say "good boy" etc.). The horse will quickly learn that doing what is asked (loping) is easier and much more enjoyable than doing the wrong thing (bucking).
The above solved my problem pretty quickly. My mare still has plenty of attitude (which is why I got a mare in the first place), but she has also developed a greater respect for me.
Hope this helps.